A molecule having both a polar group and a hydrophobic group therein, such as surfactants, poly(N-substituted acrylamide) derivatives, such as poly(N-isopropylacrylamide), poly(N-substituted methacrylamide) derivatives, copolymers of these, poly(vinyl methyl ether), partly acetylated poly(vinyl alcohol), and polypeptides (proteins and peptides), are known to have a temperature responsiveness in which the molecule satisfactorily dissolves or disperses in water at low temperatures but, upon heating to or a certain temperature or higher, the molecule gathers, shrinks, aggregates, gelates, or precipitates due to hydrophobic interaction. Such materials have been utilized as incubation materials, biomaterials such as DDS materials, adsorbents, supports for substance separation, and gelling agents. For example, MATRIGEL (trademark), which is a gelatinous protein mixture and into which a protein such as collagen has been incorporated, PLURONIC (registered trademark), which is a nonionic surfactant, and UPCELL (registered trademark), which is poly(N-isopropylacrylamide), are on the market as matrices for cell incubation, DDS materials, and culture medium bases.
Meanwhile, in many factories including electric power plants and ironworks and in apparatus having an internal combustion engine, such as motor vehicles, ships, and airplanes, a large proportion of the heat energy (about 60% of the energy in the case of thermal power generation and engines) is discarded. In recent years, more efficient energy utilization is required from the standpoint of rendering sustainable society, and there is a desire for a technique for converting waste heat into utilizable energy. A method for recovering heat energy from waste heat and reusing the recovered energy as warm water or the like (cogeneration, combined-cycle power generation, heating in motor vehicles, or the like) and a technique for converting a temperature difference into electrical energy using a thermoelectric conversion element have already been developed. However, no technique for efficiently recovering energy from a small temperature difference has been devised, and most of the waste heat (28% in cogeneration) is being discarded into the environment even at present without being utilized.
There also is a desire for a technique for separating and recovering carbon dioxide from discharge gases, from the standpoint of preventing the global warming Since carbon dioxide is readily absorbed into basic aqueous solutions, a chemical absorption method using an aqueous solution of a low-molecular weight amine is presently receiving attention. However, the aqueous solution of a low-molecular weight amine needs to be heated to an extremely high temperature when the carbon dioxide absorbed thereinto is separated therefrom, and the current chemical absorption method has an exceedingly poor energy efficiency.
Incidentally, Patent Document 1 describes a technique which has an electromotive-force layer constituted of both a polar polymer and a polar low-molecular weight compound contained in the matrix of the polymer and in which charges are generated by means of a temperature difference.